xref: /linux/net/9p/trans_virtio.c (revision 36ec807b627b4c0a0a382f0ae48eac7187d14b2b)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * The Virtio 9p transport driver
4  *
5  * This is a block based transport driver based on the lguest block driver
6  * code.
7  *
8  *  Copyright (C) 2007, 2008 Eric Van Hensbergen, IBM Corporation
9  *
10  *  Based on virtio console driver
11  *  Copyright (C) 2006, 2007 Rusty Russell, IBM Corporation
12  */
13 
14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
15 
16 #include <linux/in.h>
17 #include <linux/module.h>
18 #include <linux/net.h>
19 #include <linux/ipv6.h>
20 #include <linux/errno.h>
21 #include <linux/kernel.h>
22 #include <linux/un.h>
23 #include <linux/uaccess.h>
24 #include <linux/inet.h>
25 #include <linux/file.h>
26 #include <linux/highmem.h>
27 #include <linux/slab.h>
28 #include <net/9p/9p.h>
29 #include <linux/parser.h>
30 #include <net/9p/client.h>
31 #include <net/9p/transport.h>
32 #include <linux/scatterlist.h>
33 #include <linux/swap.h>
34 #include <linux/virtio.h>
35 #include <linux/virtio_9p.h>
36 #include "trans_common.h"
37 
38 #define VIRTQUEUE_NUM	128
39 
40 /* a single mutex to manage channel initialization and attachment */
41 static DEFINE_MUTEX(virtio_9p_lock);
42 static DECLARE_WAIT_QUEUE_HEAD(vp_wq);
43 static atomic_t vp_pinned = ATOMIC_INIT(0);
44 
45 /**
46  * struct virtio_chan - per-instance transport information
47  * @inuse: whether the channel is in use
48  * @lock: protects multiple elements within this structure
49  * @client: client instance
50  * @vdev: virtio dev associated with this channel
51  * @vq: virtio queue associated with this channel
52  * @ring_bufs_avail: flag to indicate there is some available in the ring buf
53  * @vc_wq: wait queue for waiting for thing to be added to ring buf
54  * @p9_max_pages: maximum number of pinned pages
55  * @sg: scatter gather list which is used to pack a request (protected?)
56  * @chan_list: linked list of channels
57  *
58  * We keep all per-channel information in a structure.
59  * This structure is allocated within the devices dev->mem space.
60  * A pointer to the structure will get put in the transport private.
61  *
62  */
63 
64 struct virtio_chan {
65 	bool inuse;
66 
67 	spinlock_t lock;
68 
69 	struct p9_client *client;
70 	struct virtio_device *vdev;
71 	struct virtqueue *vq;
72 	int ring_bufs_avail;
73 	wait_queue_head_t *vc_wq;
74 	/* This is global limit. Since we don't have a global structure,
75 	 * will be placing it in each channel.
76 	 */
77 	unsigned long p9_max_pages;
78 	/* Scatterlist: can be too big for stack. */
79 	struct scatterlist sg[VIRTQUEUE_NUM];
80 	/**
81 	 * @tag: name to identify a mount null terminated
82 	 */
83 	char *tag;
84 
85 	struct list_head chan_list;
86 };
87 
88 static struct list_head virtio_chan_list;
89 
90 /* How many bytes left in this page. */
91 static unsigned int rest_of_page(void *data)
92 {
93 	return PAGE_SIZE - offset_in_page(data);
94 }
95 
96 /**
97  * p9_virtio_close - reclaim resources of a channel
98  * @client: client instance
99  *
100  * This reclaims a channel by freeing its resources and
101  * resetting its inuse flag.
102  *
103  */
104 
105 static void p9_virtio_close(struct p9_client *client)
106 {
107 	struct virtio_chan *chan = client->trans;
108 
109 	mutex_lock(&virtio_9p_lock);
110 	if (chan)
111 		chan->inuse = false;
112 	mutex_unlock(&virtio_9p_lock);
113 }
114 
115 /**
116  * req_done - callback which signals activity from the server
117  * @vq: virtio queue activity was received on
118  *
119  * This notifies us that the server has triggered some activity
120  * on the virtio channel - most likely a response to request we
121  * sent.  Figure out which requests now have responses and wake up
122  * those threads.
123  *
124  * Bugs: could do with some additional sanity checking, but appears to work.
125  *
126  */
127 
128 static void req_done(struct virtqueue *vq)
129 {
130 	struct virtio_chan *chan = vq->vdev->priv;
131 	unsigned int len;
132 	struct p9_req_t *req;
133 	bool need_wakeup = false;
134 	unsigned long flags;
135 
136 	p9_debug(P9_DEBUG_TRANS, ": request done\n");
137 
138 	spin_lock_irqsave(&chan->lock, flags);
139 	while ((req = virtqueue_get_buf(chan->vq, &len)) != NULL) {
140 		if (!chan->ring_bufs_avail) {
141 			chan->ring_bufs_avail = 1;
142 			need_wakeup = true;
143 		}
144 
145 		if (len) {
146 			req->rc.size = len;
147 			p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
148 		}
149 	}
150 	spin_unlock_irqrestore(&chan->lock, flags);
151 	/* Wakeup if anyone waiting for VirtIO ring space. */
152 	if (need_wakeup)
153 		wake_up(chan->vc_wq);
154 }
155 
156 /**
157  * pack_sg_list - pack a scatter gather list from a linear buffer
158  * @sg: scatter/gather list to pack into
159  * @start: which segment of the sg_list to start at
160  * @limit: maximum segment to pack data to
161  * @data: data to pack into scatter/gather list
162  * @count: amount of data to pack into the scatter/gather list
163  *
164  * sg_lists have multiple segments of various sizes.  This will pack
165  * arbitrary data into an existing scatter gather list, segmenting the
166  * data as necessary within constraints.
167  *
168  */
169 
170 static int pack_sg_list(struct scatterlist *sg, int start,
171 			int limit, char *data, int count)
172 {
173 	int s;
174 	int index = start;
175 
176 	while (count) {
177 		s = rest_of_page(data);
178 		if (s > count)
179 			s = count;
180 		BUG_ON(index >= limit);
181 		/* Make sure we don't terminate early. */
182 		sg_unmark_end(&sg[index]);
183 		sg_set_buf(&sg[index++], data, s);
184 		count -= s;
185 		data += s;
186 	}
187 	if (index-start)
188 		sg_mark_end(&sg[index - 1]);
189 	return index-start;
190 }
191 
192 /* We don't currently allow canceling of virtio requests */
193 static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
194 {
195 	return 1;
196 }
197 
198 /* Reply won't come, so drop req ref */
199 static int p9_virtio_cancelled(struct p9_client *client, struct p9_req_t *req)
200 {
201 	p9_req_put(client, req);
202 	return 0;
203 }
204 
205 /**
206  * pack_sg_list_p - Just like pack_sg_list. Instead of taking a buffer,
207  * this takes a list of pages.
208  * @sg: scatter/gather list to pack into
209  * @start: which segment of the sg_list to start at
210  * @limit: maximum number of pages in sg list.
211  * @pdata: a list of pages to add into sg.
212  * @nr_pages: number of pages to pack into the scatter/gather list
213  * @offs: amount of data in the beginning of first page _not_ to pack
214  * @count: amount of data to pack into the scatter/gather list
215  */
216 static int
217 pack_sg_list_p(struct scatterlist *sg, int start, int limit,
218 	       struct page **pdata, int nr_pages, size_t offs, int count)
219 {
220 	int i = 0, s;
221 	int data_off = offs;
222 	int index = start;
223 
224 	BUG_ON(nr_pages > (limit - start));
225 	/*
226 	 * if the first page doesn't start at
227 	 * page boundary find the offset
228 	 */
229 	while (nr_pages) {
230 		s = PAGE_SIZE - data_off;
231 		if (s > count)
232 			s = count;
233 		BUG_ON(index >= limit);
234 		/* Make sure we don't terminate early. */
235 		sg_unmark_end(&sg[index]);
236 		sg_set_page(&sg[index++], pdata[i++], s, data_off);
237 		data_off = 0;
238 		count -= s;
239 		nr_pages--;
240 	}
241 
242 	if (index-start)
243 		sg_mark_end(&sg[index - 1]);
244 	return index - start;
245 }
246 
247 /**
248  * p9_virtio_request - issue a request
249  * @client: client instance issuing the request
250  * @req: request to be issued
251  *
252  */
253 
254 static int
255 p9_virtio_request(struct p9_client *client, struct p9_req_t *req)
256 {
257 	int err;
258 	int in, out, out_sgs, in_sgs;
259 	unsigned long flags;
260 	struct virtio_chan *chan = client->trans;
261 	struct scatterlist *sgs[2];
262 
263 	p9_debug(P9_DEBUG_TRANS, "9p debug: virtio request\n");
264 
265 	WRITE_ONCE(req->status, REQ_STATUS_SENT);
266 req_retry:
267 	spin_lock_irqsave(&chan->lock, flags);
268 
269 	out_sgs = in_sgs = 0;
270 	/* Handle out VirtIO ring buffers */
271 	out = pack_sg_list(chan->sg, 0,
272 			   VIRTQUEUE_NUM, req->tc.sdata, req->tc.size);
273 	if (out)
274 		sgs[out_sgs++] = chan->sg;
275 
276 	in = pack_sg_list(chan->sg, out,
277 			  VIRTQUEUE_NUM, req->rc.sdata, req->rc.capacity);
278 	if (in)
279 		sgs[out_sgs + in_sgs++] = chan->sg + out;
280 
281 	err = virtqueue_add_sgs(chan->vq, sgs, out_sgs, in_sgs, req,
282 				GFP_ATOMIC);
283 	if (err < 0) {
284 		if (err == -ENOSPC) {
285 			chan->ring_bufs_avail = 0;
286 			spin_unlock_irqrestore(&chan->lock, flags);
287 			err = wait_event_killable(*chan->vc_wq,
288 						  chan->ring_bufs_avail);
289 			if (err  == -ERESTARTSYS)
290 				return err;
291 
292 			p9_debug(P9_DEBUG_TRANS, "Retry virtio request\n");
293 			goto req_retry;
294 		} else {
295 			spin_unlock_irqrestore(&chan->lock, flags);
296 			p9_debug(P9_DEBUG_TRANS,
297 				 "virtio rpc add_sgs returned failure\n");
298 			return -EIO;
299 		}
300 	}
301 	virtqueue_kick(chan->vq);
302 	spin_unlock_irqrestore(&chan->lock, flags);
303 
304 	p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
305 	return 0;
306 }
307 
308 static int p9_get_mapped_pages(struct virtio_chan *chan,
309 			       struct page ***pages,
310 			       struct iov_iter *data,
311 			       int count,
312 			       size_t *offs,
313 			       int *need_drop)
314 {
315 	int nr_pages;
316 	int err;
317 
318 	if (!iov_iter_count(data))
319 		return 0;
320 
321 	if (!iov_iter_is_kvec(data)) {
322 		int n;
323 		/*
324 		 * We allow only p9_max_pages pinned. We wait for the
325 		 * Other zc request to finish here
326 		 */
327 		if (atomic_read(&vp_pinned) >= chan->p9_max_pages) {
328 			err = wait_event_killable(vp_wq,
329 			      (atomic_read(&vp_pinned) < chan->p9_max_pages));
330 			if (err == -ERESTARTSYS)
331 				return err;
332 		}
333 		n = iov_iter_get_pages_alloc2(data, pages, count, offs);
334 		if (n < 0)
335 			return n;
336 		*need_drop = 1;
337 		nr_pages = DIV_ROUND_UP(n + *offs, PAGE_SIZE);
338 		atomic_add(nr_pages, &vp_pinned);
339 		return n;
340 	} else {
341 		/* kernel buffer, no need to pin pages */
342 		int index;
343 		size_t len;
344 		void *p;
345 
346 		/* we'd already checked that it's non-empty */
347 		while (1) {
348 			len = iov_iter_single_seg_count(data);
349 			if (likely(len)) {
350 				p = data->kvec->iov_base + data->iov_offset;
351 				break;
352 			}
353 			iov_iter_advance(data, 0);
354 		}
355 		if (len > count)
356 			len = count;
357 
358 		nr_pages = DIV_ROUND_UP((unsigned long)p + len, PAGE_SIZE) -
359 			   (unsigned long)p / PAGE_SIZE;
360 
361 		*pages = kmalloc_array(nr_pages, sizeof(struct page *),
362 				       GFP_NOFS);
363 		if (!*pages)
364 			return -ENOMEM;
365 
366 		*need_drop = 0;
367 		p -= (*offs = offset_in_page(p));
368 		for (index = 0; index < nr_pages; index++) {
369 			if (is_vmalloc_addr(p))
370 				(*pages)[index] = vmalloc_to_page(p);
371 			else
372 				(*pages)[index] = kmap_to_page(p);
373 			p += PAGE_SIZE;
374 		}
375 		iov_iter_advance(data, len);
376 		return len;
377 	}
378 }
379 
380 static void handle_rerror(struct p9_req_t *req, int in_hdr_len,
381 			  size_t offs, struct page **pages)
382 {
383 	unsigned size, n;
384 	void *to = req->rc.sdata + in_hdr_len;
385 
386 	// Fits entirely into the static data?  Nothing to do.
387 	if (req->rc.size < in_hdr_len || !pages)
388 		return;
389 
390 	// Really long error message?  Tough, truncate the reply.  Might get
391 	// rejected (we can't be arsed to adjust the size encoded in header,
392 	// or string size for that matter), but it wouldn't be anything valid
393 	// anyway.
394 	if (unlikely(req->rc.size > P9_ZC_HDR_SZ))
395 		req->rc.size = P9_ZC_HDR_SZ;
396 
397 	// data won't span more than two pages
398 	size = req->rc.size - in_hdr_len;
399 	n = PAGE_SIZE - offs;
400 	if (size > n) {
401 		memcpy_from_page(to, *pages++, offs, n);
402 		offs = 0;
403 		to += n;
404 		size -= n;
405 	}
406 	memcpy_from_page(to, *pages, offs, size);
407 }
408 
409 /**
410  * p9_virtio_zc_request - issue a zero copy request
411  * @client: client instance issuing the request
412  * @req: request to be issued
413  * @uidata: user buffer that should be used for zero copy read
414  * @uodata: user buffer that should be used for zero copy write
415  * @inlen: read buffer size
416  * @outlen: write buffer size
417  * @in_hdr_len: reader header size, This is the size of response protocol data
418  *
419  */
420 static int
421 p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
422 		     struct iov_iter *uidata, struct iov_iter *uodata,
423 		     int inlen, int outlen, int in_hdr_len)
424 {
425 	int in, out, err, out_sgs, in_sgs;
426 	unsigned long flags;
427 	int in_nr_pages = 0, out_nr_pages = 0;
428 	struct page **in_pages = NULL, **out_pages = NULL;
429 	struct virtio_chan *chan = client->trans;
430 	struct scatterlist *sgs[4];
431 	size_t offs = 0;
432 	int need_drop = 0;
433 	int kicked = 0;
434 
435 	p9_debug(P9_DEBUG_TRANS, "virtio request\n");
436 
437 	if (uodata) {
438 		__le32 sz;
439 		int n = p9_get_mapped_pages(chan, &out_pages, uodata,
440 					    outlen, &offs, &need_drop);
441 		if (n < 0) {
442 			err = n;
443 			goto err_out;
444 		}
445 		out_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
446 		if (n != outlen) {
447 			__le32 v = cpu_to_le32(n);
448 			memcpy(&req->tc.sdata[req->tc.size - 4], &v, 4);
449 			outlen = n;
450 		}
451 		/* The size field of the message must include the length of the
452 		 * header and the length of the data.  We didn't actually know
453 		 * the length of the data until this point so add it in now.
454 		 */
455 		sz = cpu_to_le32(req->tc.size + outlen);
456 		memcpy(&req->tc.sdata[0], &sz, sizeof(sz));
457 	} else if (uidata) {
458 		int n = p9_get_mapped_pages(chan, &in_pages, uidata,
459 					    inlen, &offs, &need_drop);
460 		if (n < 0) {
461 			err = n;
462 			goto err_out;
463 		}
464 		in_nr_pages = DIV_ROUND_UP(n + offs, PAGE_SIZE);
465 		if (n != inlen) {
466 			__le32 v = cpu_to_le32(n);
467 			memcpy(&req->tc.sdata[req->tc.size - 4], &v, 4);
468 			inlen = n;
469 		}
470 	}
471 	WRITE_ONCE(req->status, REQ_STATUS_SENT);
472 req_retry_pinned:
473 	spin_lock_irqsave(&chan->lock, flags);
474 
475 	out_sgs = in_sgs = 0;
476 
477 	/* out data */
478 	out = pack_sg_list(chan->sg, 0,
479 			   VIRTQUEUE_NUM, req->tc.sdata, req->tc.size);
480 
481 	if (out)
482 		sgs[out_sgs++] = chan->sg;
483 
484 	if (out_pages) {
485 		sgs[out_sgs++] = chan->sg + out;
486 		out += pack_sg_list_p(chan->sg, out, VIRTQUEUE_NUM,
487 				      out_pages, out_nr_pages, offs, outlen);
488 	}
489 
490 	/*
491 	 * Take care of in data
492 	 * For example TREAD have 11.
493 	 * 11 is the read/write header = PDU Header(7) + IO Size (4).
494 	 * Arrange in such a way that server places header in the
495 	 * allocated memory and payload onto the user buffer.
496 	 */
497 	in = pack_sg_list(chan->sg, out,
498 			  VIRTQUEUE_NUM, req->rc.sdata, in_hdr_len);
499 	if (in)
500 		sgs[out_sgs + in_sgs++] = chan->sg + out;
501 
502 	if (in_pages) {
503 		sgs[out_sgs + in_sgs++] = chan->sg + out + in;
504 		pack_sg_list_p(chan->sg, out + in, VIRTQUEUE_NUM,
505 			       in_pages, in_nr_pages, offs, inlen);
506 	}
507 
508 	BUG_ON(out_sgs + in_sgs > ARRAY_SIZE(sgs));
509 	err = virtqueue_add_sgs(chan->vq, sgs, out_sgs, in_sgs, req,
510 				GFP_ATOMIC);
511 	if (err < 0) {
512 		if (err == -ENOSPC) {
513 			chan->ring_bufs_avail = 0;
514 			spin_unlock_irqrestore(&chan->lock, flags);
515 			err = wait_event_killable(*chan->vc_wq,
516 						  chan->ring_bufs_avail);
517 			if (err  == -ERESTARTSYS)
518 				goto err_out;
519 
520 			p9_debug(P9_DEBUG_TRANS, "Retry virtio request\n");
521 			goto req_retry_pinned;
522 		} else {
523 			spin_unlock_irqrestore(&chan->lock, flags);
524 			p9_debug(P9_DEBUG_TRANS,
525 				 "virtio rpc add_sgs returned failure\n");
526 			err = -EIO;
527 			goto err_out;
528 		}
529 	}
530 	virtqueue_kick(chan->vq);
531 	spin_unlock_irqrestore(&chan->lock, flags);
532 	kicked = 1;
533 	p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
534 	err = wait_event_killable(req->wq,
535 			          READ_ONCE(req->status) >= REQ_STATUS_RCVD);
536 	// RERROR needs reply (== error string) in static data
537 	if (READ_ONCE(req->status) == REQ_STATUS_RCVD &&
538 	    unlikely(req->rc.sdata[4] == P9_RERROR))
539 		handle_rerror(req, in_hdr_len, offs, in_pages);
540 
541 	/*
542 	 * Non kernel buffers are pinned, unpin them
543 	 */
544 err_out:
545 	if (need_drop) {
546 		if (in_pages) {
547 			p9_release_pages(in_pages, in_nr_pages);
548 			atomic_sub(in_nr_pages, &vp_pinned);
549 		}
550 		if (out_pages) {
551 			p9_release_pages(out_pages, out_nr_pages);
552 			atomic_sub(out_nr_pages, &vp_pinned);
553 		}
554 		/* wakeup anybody waiting for slots to pin pages */
555 		wake_up(&vp_wq);
556 	}
557 	kvfree(in_pages);
558 	kvfree(out_pages);
559 	if (!kicked) {
560 		/* reply won't come */
561 		p9_req_put(client, req);
562 	}
563 	return err;
564 }
565 
566 static ssize_t p9_mount_tag_show(struct device *dev,
567 				struct device_attribute *attr, char *buf)
568 {
569 	struct virtio_chan *chan;
570 	struct virtio_device *vdev;
571 	int tag_len;
572 
573 	vdev = dev_to_virtio(dev);
574 	chan = vdev->priv;
575 	tag_len = strlen(chan->tag);
576 
577 	memcpy(buf, chan->tag, tag_len + 1);
578 
579 	return tag_len + 1;
580 }
581 
582 static DEVICE_ATTR(mount_tag, 0444, p9_mount_tag_show, NULL);
583 
584 /**
585  * p9_virtio_probe - probe for existence of 9P virtio channels
586  * @vdev: virtio device to probe
587  *
588  * This probes for existing virtio channels.
589  *
590  */
591 
592 static int p9_virtio_probe(struct virtio_device *vdev)
593 {
594 	__u16 tag_len;
595 	char *tag;
596 	int err;
597 	struct virtio_chan *chan;
598 
599 	if (!vdev->config->get) {
600 		dev_err(&vdev->dev, "%s failure: config access disabled\n",
601 			__func__);
602 		return -EINVAL;
603 	}
604 
605 	chan = kmalloc(sizeof(struct virtio_chan), GFP_KERNEL);
606 	if (!chan) {
607 		pr_err("Failed to allocate virtio 9P channel\n");
608 		err = -ENOMEM;
609 		goto fail;
610 	}
611 
612 	chan->vdev = vdev;
613 
614 	/* We expect one virtqueue, for requests. */
615 	chan->vq = virtio_find_single_vq(vdev, req_done, "requests");
616 	if (IS_ERR(chan->vq)) {
617 		err = PTR_ERR(chan->vq);
618 		goto out_free_chan;
619 	}
620 	chan->vq->vdev->priv = chan;
621 	spin_lock_init(&chan->lock);
622 
623 	sg_init_table(chan->sg, VIRTQUEUE_NUM);
624 
625 	chan->inuse = false;
626 	if (virtio_has_feature(vdev, VIRTIO_9P_MOUNT_TAG)) {
627 		virtio_cread(vdev, struct virtio_9p_config, tag_len, &tag_len);
628 	} else {
629 		err = -EINVAL;
630 		goto out_free_vq;
631 	}
632 	tag = kzalloc(tag_len + 1, GFP_KERNEL);
633 	if (!tag) {
634 		err = -ENOMEM;
635 		goto out_free_vq;
636 	}
637 
638 	virtio_cread_bytes(vdev, offsetof(struct virtio_9p_config, tag),
639 			   tag, tag_len);
640 	chan->tag = tag;
641 	err = sysfs_create_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
642 	if (err) {
643 		goto out_free_tag;
644 	}
645 	chan->vc_wq = kmalloc(sizeof(wait_queue_head_t), GFP_KERNEL);
646 	if (!chan->vc_wq) {
647 		err = -ENOMEM;
648 		goto out_remove_file;
649 	}
650 	init_waitqueue_head(chan->vc_wq);
651 	chan->ring_bufs_avail = 1;
652 	/* Ceiling limit to avoid denial of service attacks */
653 	chan->p9_max_pages = nr_free_buffer_pages()/4;
654 
655 	virtio_device_ready(vdev);
656 
657 	mutex_lock(&virtio_9p_lock);
658 	list_add_tail(&chan->chan_list, &virtio_chan_list);
659 	mutex_unlock(&virtio_9p_lock);
660 
661 	/* Let udev rules use the new mount_tag attribute. */
662 	kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
663 
664 	return 0;
665 
666 out_remove_file:
667 	sysfs_remove_file(&vdev->dev.kobj, &dev_attr_mount_tag.attr);
668 out_free_tag:
669 	kfree(tag);
670 out_free_vq:
671 	vdev->config->del_vqs(vdev);
672 out_free_chan:
673 	kfree(chan);
674 fail:
675 	return err;
676 }
677 
678 
679 /**
680  * p9_virtio_create - allocate a new virtio channel
681  * @client: client instance invoking this transport
682  * @devname: string identifying the channel to connect to (unused)
683  * @args: args passed from sys_mount() for per-transport options (unused)
684  *
685  * This sets up a transport channel for 9p communication.  Right now
686  * we only match the first available channel, but eventually we could look up
687  * alternate channels by matching devname versus a virtio_config entry.
688  * We use a simple reference count mechanism to ensure that only a single
689  * mount has a channel open at a time.
690  *
691  */
692 
693 static int
694 p9_virtio_create(struct p9_client *client, const char *devname, char *args)
695 {
696 	struct virtio_chan *chan;
697 	int ret = -ENOENT;
698 	int found = 0;
699 
700 	if (devname == NULL)
701 		return -EINVAL;
702 
703 	mutex_lock(&virtio_9p_lock);
704 	list_for_each_entry(chan, &virtio_chan_list, chan_list) {
705 		if (!strcmp(devname, chan->tag)) {
706 			if (!chan->inuse) {
707 				chan->inuse = true;
708 				found = 1;
709 				break;
710 			}
711 			ret = -EBUSY;
712 		}
713 	}
714 	mutex_unlock(&virtio_9p_lock);
715 
716 	if (!found) {
717 		pr_err("no channels available for device %s\n", devname);
718 		return ret;
719 	}
720 
721 	client->trans = (void *)chan;
722 	client->status = Connected;
723 	chan->client = client;
724 
725 	return 0;
726 }
727 
728 /**
729  * p9_virtio_remove - clean up resources associated with a virtio device
730  * @vdev: virtio device to remove
731  *
732  */
733 
734 static void p9_virtio_remove(struct virtio_device *vdev)
735 {
736 	struct virtio_chan *chan = vdev->priv;
737 	unsigned long warning_time;
738 
739 	mutex_lock(&virtio_9p_lock);
740 
741 	/* Remove self from list so we don't get new users. */
742 	list_del(&chan->chan_list);
743 	warning_time = jiffies;
744 
745 	/* Wait for existing users to close. */
746 	while (chan->inuse) {
747 		mutex_unlock(&virtio_9p_lock);
748 		msleep(250);
749 		if (time_after(jiffies, warning_time + 10 * HZ)) {
750 			dev_emerg(&vdev->dev,
751 				  "p9_virtio_remove: waiting for device in use.\n");
752 			warning_time = jiffies;
753 		}
754 		mutex_lock(&virtio_9p_lock);
755 	}
756 
757 	mutex_unlock(&virtio_9p_lock);
758 
759 	virtio_reset_device(vdev);
760 	vdev->config->del_vqs(vdev);
761 
762 	sysfs_remove_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
763 	kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
764 	kfree(chan->tag);
765 	kfree(chan->vc_wq);
766 	kfree(chan);
767 
768 }
769 
770 static struct virtio_device_id id_table[] = {
771 	{ VIRTIO_ID_9P, VIRTIO_DEV_ANY_ID },
772 	{ 0 },
773 };
774 
775 static unsigned int features[] = {
776 	VIRTIO_9P_MOUNT_TAG,
777 };
778 
779 /* The standard "struct lguest_driver": */
780 static struct virtio_driver p9_virtio_drv = {
781 	.feature_table  = features,
782 	.feature_table_size = ARRAY_SIZE(features),
783 	.driver.name    = KBUILD_MODNAME,
784 	.id_table	= id_table,
785 	.probe		= p9_virtio_probe,
786 	.remove		= p9_virtio_remove,
787 };
788 
789 static struct p9_trans_module p9_virtio_trans = {
790 	.name = "virtio",
791 	.create = p9_virtio_create,
792 	.close = p9_virtio_close,
793 	.request = p9_virtio_request,
794 	.zc_request = p9_virtio_zc_request,
795 	.cancel = p9_virtio_cancel,
796 	.cancelled = p9_virtio_cancelled,
797 	/*
798 	 * We leave one entry for input and one entry for response
799 	 * headers. We also skip one more entry to accommodate, address
800 	 * that are not at page boundary, that can result in an extra
801 	 * page in zero copy.
802 	 */
803 	.maxsize = PAGE_SIZE * (VIRTQUEUE_NUM - 3),
804 	.pooled_rbuffers = false,
805 	.def = 1,
806 	.owner = THIS_MODULE,
807 };
808 
809 /* The standard init function */
810 static int __init p9_virtio_init(void)
811 {
812 	int rc;
813 
814 	INIT_LIST_HEAD(&virtio_chan_list);
815 
816 	v9fs_register_trans(&p9_virtio_trans);
817 	rc = register_virtio_driver(&p9_virtio_drv);
818 	if (rc)
819 		v9fs_unregister_trans(&p9_virtio_trans);
820 
821 	return rc;
822 }
823 
824 static void __exit p9_virtio_cleanup(void)
825 {
826 	unregister_virtio_driver(&p9_virtio_drv);
827 	v9fs_unregister_trans(&p9_virtio_trans);
828 }
829 
830 module_init(p9_virtio_init);
831 module_exit(p9_virtio_cleanup);
832 MODULE_ALIAS_9P("virtio");
833 
834 MODULE_DEVICE_TABLE(virtio, id_table);
835 MODULE_AUTHOR("Eric Van Hensbergen <ericvh@gmail.com>");
836 MODULE_DESCRIPTION("Virtio 9p Transport");
837 MODULE_LICENSE("GPL");
838